Muscle tone and Hypotonia

All of the muscles in our bodies have a resting muscle tone. Muscle tone is a muscle’s

potential ability to respond or counter an outside force, a stretch, or a change in direction

of the muscle. Muscle tone is involuntary and directly related to a child’s inherent neural

wiring in which the brain perceives the positions of the muscles. With an intact

neuromuscular system, the muscles can adjust to immediate postural or limb changes and

maintain a child’s posture or arm and leg position upright against gravity.

Appropriate muscle tone enables a child to respond quickly to an outside force either

through balance responses/righting reactions or protective reactions. It also allows a

child’s muscles to quickly relax once the perceived change is gone. A child with

hypotonia has muscles that are slow to initiate a contraction against an outside force, and

also cannot sustain a muscle contraction as long. In other words, the muscles “relax”

quicker despite that the outside force may still be present. Muscle strength is different in

that it increases with voluntary repetitions of movement (e.g. 10 repetitions of biceps

curls). Muscle tone improves with a more comprehensive treatment approach directed to

increase the “alert state” of the muscles themselves. 

Hypotonia or low muscle tone can be based in the muscles themselves or within the

central nervous system. If the low muscle tone is derived from the muscles (e.g. muscular

dystrophy), then there is a dysfunction within the muscles. The receptors within the

muscles are not getting the proper signal to the brain to alert the child’s system of changes

in position. If the hypotonia is based within the central nervous system, complex feedback

loops of sensory processing and motor output are implicated. There are often sensory

processing deficits (vestibular, proprioceptive and tactile) that are not alerting the brain of

changes in body position. Also, the child may have a praxis or motor planning deficit in

which the child’s body cannot formulate the proper motor response.

A child with hypotonia may have mild and benign developmental delays or could

potentially have a serious muscular, genetic or neurological illness. Regardless of the

cause, these children are at risk for developing poor balance and coordination, permanent

orthopedic abnormalities, learning disabilities, and language delays. The most appropriate

treatment for a child with hypotonia is immediate early intervention and therapy

An infant with hypotonia may have poor head control and resist propping on their

tummies when awake. Babies will often seem to “slip out of your hands” and have

trouble “stiffening” their bodies when you carry them. When lying on their backs, babies

with hypotonia will often rest with their arms and legs extended outward and sometimes

resist bearing weight on their feet when held upright on your legs. Younger children with

hypotonia may tend to lean excessively forward when they are sitting up. Older toddlers

and children will tend to “W-sit” to reduce the challenge to their postural muscles.

Children with low muscle tone may have difficulty learning to roll, sit, crawl and walk

independently. Because these gross motor skills are the building blocks for later higher

level gross and fine motor skills, it is recommended that children receive therapy to

facilitate appropriate motor development. Muscle tone improves with a comprehensive

treatment approach to improve postural control and address issues within the nervous

system that help the brain perceive where the body is in space. Therapy often focuses on

improving the delayed postural responses and protective reactions that are typical in

children with hypotonia. Therapy will also focus on improving sensory processing in

order to improve body awareness, balance and motor planning. Because low muscle tone

is also associated with laxity or looseness in a child’s ligaments, therapy also aims to

improve overall muscle strength to increase the support around the joints in the arms and

legs. If you have any further questions about hypotonia, please do not hesitate to contact

us for a consultation or physical therapy screening to determine whether your child will

benefit from therapy.